This invention refers to a supporting structure for sheet material, especially sheet metal material cut out by a laser device positioned above the sheet material and focused on it, as defined in the preamble of claim 1.
In this connection, means for movement between the laser device and the sheet metal and/or the supporting structure are provided, permitting the laser device to be guided over the desired cutting positions. The cuts here can be curves or quasi bores formed by round cutouts.
The same problems also exist in other devices in which welding or cutting operations are initiated through the development of heat. These operations affect the underside of the sheet metal, therefore also affecting the supporting structure for the sheet metal.
In one possible version, the laser device is stationary and the sheet metal is moved in two perpendicular directions over corresponding supports in accordance with the desired cutouts. In this case a gap is provided beneath the laser device to prevent damage to the supporting structure or soiling of the underside of the sheet metal. However, moving heavy bodies at the desired high rate of speed results in loss of precision. Therefore, a preferred method is to move the relatively light-weight laser device over a stationary sheet metal support. However, the problem with this in particular is that the laser beam also adversely affects the supporting structure of the sheet metal, so that after a relatively short time a large number of molten metal particles are caused to adhere to it through the action of sparks, etc. The molten sheet metal particles impacting the underside of the sheet metal must be removed in laborious subsequent treatments. Moreover, the supporting structure itself is usually only heat resistant for a short time, which causes instances of melting and a relatively short life. Using highly heat-resistant material is unfeasible due to the costs.
To alleviate the problems described above, the Swiss company Bystronic, for example, has manufactured supporting structures for sheet metal that substantially comprise vertically mounted parallel rows of identical narrow sheet strips having raised integrated support areas for the sheet metal between recessed grooves. Thus, the molten material falling into the recessed grooves causes relatively little damage. Nonetheless, the support areas in particular still constitute a problem zone leading to a reduced lifetime and to contamination of the underside of the sheet metal. Various remedies, such as designing the support areas of the supporting structure for the sheet metal as rollers, have not been fully satisfactory either.
DE 44 46 975 A1 describes a supporting grate for workpieces. This grate, for example, can comprise supporting pins that can be mounted on lower beams arranged side by side. These supporting pins are relatively broad and conical, for which reason the sheet metal runs the risk that sheet material sputtered through the sheet metal by the laser can be reflected from below onto the underside of the sheet metal. If the supporting pins coincide with a laser beam cutting point, they can not withstand the effects of the heat and have a correspondingly short life. The laser machining head can only be moved in a single straight line; a corresponding straight movement of the supporting table in a direction offset by 90xc2x0 is provided. The cutting itself is performed at one single cutting place. The invention relates in particular to the dropping of sheet metal pieces supported at the most at one or two points, and to their removal of the same. When the last point of the sheet metal part to be cut out is cut through, the sheet metal part tilts down, thus causing a rough cut surface at this end section. This results in diminished quality and requires subsequent treatment.
JP 63-52 790 A, Patent Abstracts of Japan M-723, 1988, vol. 12, no. 269, describes a two-part supporting pin in a support grate, the upper portion of the pin comprising a conical insert of a high-melting material such as molybdenum or tungsten. The wide conical angle and the low cone height cause the material melted and flung downward by the laser device to be reflected back onto the underside of the sheet metal. The lower end of the conical needle tip is a peg which is inserted into the actual hollow-cylindrical needle. The structure is relatively broad and can not be precisely adjusted. The space required for the relatively wide cone base does not allow for very small sheet metal parts down to less than one square centimeter in area to be sturdily supported by three points.
The object of the invention is to provide a supporting structure for sheet metal in accordance with the preamble of claim 1, in such a manner that the lifetime is increased and damage to the underside of the sheet metal is avoided, particularly in the case of a movable laser device over a stationary sheet metal supporting structure.
This object is carried out in accordance with the invention by the features of claim 1. Further embodiments of the invention are protected by the subclaims.
In the subject matter of the invention a needle or similar thin material is mounted on the support areas. The sheet metal is laid onto the free ends of these needles, all of which of course am equal in length. These needles, the mass of which constitutes only a minute proportion, are made of a material such as tungsten that is more heat-resistant than the sheet strips. Of course, they have no eyes as in sewing needles.
The remaining material, namely for the sheet strips, can consist of rustproof steel such as chromium-nickel steel. However, this means that after a rather long operating time, the very hot sheet metal particles heated in the cutting operation, namely the laser cutting wastes, settle on certain parts of the sheet metal supporting structure, namely on the sheet strips, after having been blown out of and catapulted from the kerf of the sheet metal workpiece and striking the sheet strips. More particles can accumulate on this in the course of time; for instance, they can become welded to the supporting structure, so that the raised arrangement of the needle tips over the support areas levels off to such an extent that, contrary to the aim of the invention, waste particles can again contact the underside of the sheet metal, causing the aforementioned damage.
These problems in long-time operation can surprisingly be prevented for the most part by selection of a more suitable material. This material should be substantially different from the material of the sheet metal being processed, which usually can be stainless steel or chromium-nickel steel for the main intended purpose. A material should be selected that does not enter into a chemical and/or physical bondxe2x80x94for instance being fused or welded on, etc.xe2x80x94with the hot sheet metal particles striking it from the laser cutting gap.
Possibly, with regard to the periodic system of elements there can be a certain relationship between the materials selected for the sheet strips of the sheet metal-supporting structure and for the sheet metal being machined. Surprisingly, if a substantially softer material is selected for the sheet metal-supporting structure, one with a substantially lower melting point, a far higher thermal conductivity and as high a specific thermal capacitance as possible, such as copper in the case of chromium-nickel steel, has proved to be particularly advantageous. The chromium-nickel waste particles do not bond with the copper supporting structure, but rather simply drop off.
It must be mentioned in this connection that of course the machining time required by a laser cutting device decreases as the electric power increases, and thicker sheets can be processed more quickly in this manner. However, this also results in a corresponding increase in larger, hot sheet metal particles blown out of the kerf as laser cutting wastes and striking the supporting structure. Thus, the problems explained above grow with increased use of higher-power laser cutting devices and thicker sheet metals to be machined.
The needles mounted on the integrated support areas project upward from the same by approximately one to ten centimeters, preferably two and one-half to three centimeters. This distance is generally sufficient to definitively rule out damage to the sheet strip, not only at the recessed grooves, but also the higher support areas. Moreover, these areas are limited to the minimum surface area required to enable: a secure, defined mounting of the individual needles at a uniform height.
In one embodiment of the invention the following structure is provided:
A strip is fixed to a lower mounting base for attachment to a support bed. The top portion of the strip is bent down by 180xc2x0, resulting in two sheet sides. It includes at its top the wide, recessed grooves and the narrow, raised, integrated support areas for the needles. An upper through hole for the needle is provided in the support areas and extends between the two bent down sheet sides. A common, continuous outer guide for all needles is provided in these through holes.
Below the common outer guide there is a common inner guide which also effects an adjustment of the needles, in a direction perpendicular to that of the outer guide. In addition, a common lower stop is provided for all needles to achieve a defined end stop. A broken or faulty needle can be removed and replaced through a lateral orifice located in the two sheet sides, below each needle in the area of the stop.
The needles are in one piece and solid, and their upper ends taper to a point in a conventional manner at the supporting surface. They are extremely thin and so long that no sheet metal material splattered by the laser cutting process can find its way from them back up to the underside of the sheet metal. The diameter of the needles is between one and three millimeters.
The specially designed support areas with recessed grooves between them, and the thin needles make an extremely high needle density possible. This means that even in the case of very small cut-out areas down to one square centimeter and less, a very sturdy three-point support becomes possible. By this means it is possible to avoid the undesirable breaking off of the sheet metal cutout at the last cutting area which causes a rough flawed surface at this point.
The configuration of the support areas, recessed grooves, and needles is preferably such that laterally engaging grippers can lift up the cut-out sheet metal parts and empty them into a container in a conventional or also a specialized manner.
Although the supporting structure is suitable for all sheet metals and for different application purposes, it is preferably utilized in apparatus with a stationary support for the sheet metal and a movable laser device arranged above the same. The laser device in that case is moved horizontally in two perpendicular directions by means of control devices.